AWS Lambda NodeJs unable to return response

Question

I am trying to implement a simple Node Js example on AWS Lambda,
The code has a sample example of Async library.
The code works fine, but from some reason the Lambda Function return null response.
I am new to Node as well, please help.

Following is the code -

var async = require('async');

exports.handler = async (event, context, callback) => {
    async.waterfall([
        function(callback) {
            console.log("ONE");
            callback(null, 1);
        },
        function(resp, callback) {
            console.log("TWO : ", resp);
            callback(null, 2);
        },
        function(resp, callback){
            console.log("THREE : ", resp);
            callback(null, "Done");
        }
    ],
    function(err, resp) {
        let response = {};
        if (err) {
            console.log("Error",err);
            response = {
                statusCode: 500,
                body: JSON.stringify('Error!'),
            };
            return response;
        } else {
            console.log("Success",resp);
            response = {
                statusCode: 200,
                body: JSON.stringify('Ok!'),
            };
            return response;
        }
    });
};

Following are the CloudWatch logs -

START RequestId: ab9aa426-dfc9-44ac-8d96-a4f102e30861 Version: $LATEST
2019-03-21T15:15:26.597Z    ab9aa426-dfc9-44ac-8d96-a4f102e30861    ONE
2019-03-21T15:15:26.597Z    ab9aa426-dfc9-44ac-8d96-a4f102e30861    TWO :  1
2019-03-21T15:15:26.597Z    ab9aa426-dfc9-44ac-8d96-a4f102e30861    THREE :  2
2019-03-21T15:15:26.597Z    ab9aa426-dfc9-44ac-8d96-a4f102e30861    Success Done
END RequestId: ab9aa426-dfc9-44ac-8d96-a4f102e30861
REPORT RequestId: ab9aa426-dfc9-44ac-8d96-a4f102e30861  Duration: 37.28 ms  Billed Duration: 100 ms     Memory Size: 128 MB Max Memory Used: 67 MB

I used the sample Node blueprint, which works fine -

exports.handler = async (event) => {
    // TODO implement
    const response = {
        statusCode: 200,
        body: JSON.stringify('Hello from Lambda!'),
    };
    return response;
};

Wouldn't there be a conflict here with async from the library async.js and native async? — Alexander Staroselsky
– Alexander Staroselsky, Commented Mar 21, 2019 at 15:24
@AniruddhaRaje When you invoke it from the console, what invocation type are you using? Event? RequestResponse? — gillyhl
– gillyhl, Commented Mar 21, 2019 at 15:25
I used the default params but, my code doesn't process them, just does a simple async lib use and should return the "response" object — Dev1ce
– Dev1ce, Commented Mar 21, 2019 at 15:28

yerzhan7 · Accepted Answer · 2019-10-22 18:30:31Z

6

Since you're already using Node 8, you don't need to use the outdated, confusing callback approach anymore. Use await instead

exports.handler = async (event) => {
    try {
        await somePromise1 
        await somePromise2
        await somePromise3 
        console.log("Success", resp);
        response = {
            statusCode: 200,
            body: JSON.stringify('Ok!'),
        };
        return response;
    } catch (err) {
        console.log("Error", err);
        response = {
            statusCode: 500,
            body: JSON.stringify(err),
        };
        return response;
    }
};

where somePromise1, somePromise2 and somePromise3 are your promisified callbacks.

3 Comments

Jeremy Thille Over a year ago

But Promise.all launches all the Promises in parallel (I believe), while async.waterfall launches each Promise after the other, passing the result to the next. But I agree async/await is the way to go now, compared to a library like async.js (which, despite the name, is completely different!)

Thales Minussi Over a year ago

I initially had this post as await promise1 await promise2 and await promise3 because I thought waterfall was running them sequentially. Then I was like: "Nah, this must be in parallel", so I changed to Promise.all. Then you dropped this comment and I checked the docs and you're right, it's sequential, so I am changing it back to three awaits instead. Thanks for your input!

Thales Minussi Over a year ago

Thank you very much, sir! :)

ttulka · Accepted Answer · 2019-03-21 15:33:28Z

Try to remove the async from the handler and use callback instead of return:

var async = require('async');

exports.handler = (event, context, callback) => {
    async.waterfall([
        function(callback) {
            console.log("ONE");
            callback(null, 1);
        },
        function(resp, callback) {
            console.log("TWO : ", resp);
            callback(null, 2);
        },
        function(resp, callback){
            console.log("THREE : ", resp);
            callback(null, "Done");
        }
    ],
    function(err, resp) {
        let response = {};
        if (err) {
            console.log("Error",err);
            callback(null, {
                statusCode: 500,
                body: 'Error!',
            });
        } else {
            console.log("Success",resp);
            callback(null, {
                statusCode: 200,
                body: 'Ok!',
            });
        }
    });
};

حمزہ لیاقت · Accepted Answer · 2024-07-03 09:12:47Z

1

to return the response use this : return { statusCode: 200, body: JSON.stringify(response) }

answered Jul 3, 2024 at 9:12

حمزہ لیاقت

335 bronze badges

1 Comment

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